My friend, Richard Mouw, a philosopher and former president of Fuller Theological Seminary, has raised an important challenge about the use of counterexamples when making one’s case on certain controversial moral and political questions.

He shares one of the arguments he employs to explain to his friends why he opposes the legal recognition of same-sex “marriage” (SSM): “If we are to operate as a society on the assumption that any sincerely held view about what constitutes a marriage should be granted status in our laws and practices, I have asked, what would keep us from legalizing plural marriages, or even incestuous ones?” Mouw says that his question is often “met with disdain,” with the retort, “[C]an’t you do better than a ‘slippery slope’ argument?”